Technical Field
[0001] The present invention relates to a wireless communication system, a base station
apparatus, a user terminal, and a channel state information measurement method in
a next-generation mobile communication system.
Background Art
[0002] In a UMTS (Universal Mobile Telecommunications System) network, attempts are made
to optimize features of the system, which are based on W-CDMA (Wideband Code Division
Multiple Access), by adopting HSDPA (High Speed Downlink Packet Access) and HSUPA
(High Speed Uplink Packet Access), for the purposes of improving spectral efficiency
and improving the data rates. With this UMTS network, long-term evolution (LTE) is
under study for the purposes of further increasing high-speed data rates, providing
low delay, and so on (non-patent literature 1).
[0003] In the third-generation system, a transmission rate of maximum approximately 2 Mbps
can be achieved on the downlink by using a fixed band of approximately 5 MHz. Meanwhile,
in an LTE system, it is possible to achieve a transmission rate of about maximum 300
Mbps on the downlink and about 75 Mbps on the uplink by using a variable band which
ranges from 1.4 MHz to 20 MHz. Furthermore, with the UMTS network, a successor system
of an LTE system is also under study for the purpose of achieving further broadbandization
and higher speed (for example, referred to as "LTE advanced" or may be referred to
as "LTE enhancement" (hereinafter ("LTE-A")).
[0004] In the downlink of an LTE system (for example, Rel. 8 LTE), CRSs (Cell-specific Reference
Signals), which are associated with cell IDs, are defined. These CRSs are used to
demodulate user data, and, besides, used to measure downlink channel quality (CQI:
Channel Quality Indicator) for scheduling and adaptive control, and so on. Meanwhile,
in the downlink of the successor system (for example, Rel. 10 LTE) of LTE, a CSI-RS
(Channel State Information - Reference Signal) is under study for dedicated use of
CSI (Channel State Information) measurement.
[0005] 3GPP draft R1-113773 describes the reliance on CSI-RS for both channel and interference estimation as
a problem. As to increase the number of resources for interference measurement, the
document proposes two alternatives namely either introduction of additional non-zero
power CSI-RS resources for interference measurement or introduction of additional
zero power CSI-RS resources for interference measurement.
[0006] 3GPP draft R1-114399 describes that channel estimation is performed from non-zero power CSI-RS but interference
is estimated from separately configured zero power CSI-RS.
[0007] 3GPP draft R1-114228 describes two interference measurement for downlink CoMP for the same meeting discusses
interference measurement on muted resources.
[0008] 3GPP draft R1-113051 describes point selection and CSI feedback for CoMP operation. It is proposed that
Multiple CSI-RS configurations with non-zero transmission power in CSI-RS-Config RRC
information element should be allowed for CoMP operation.
[0009] 3GPP draft R1-113034 describes DL MIMO CSI enhancement for multiple points. It is proposed that the non-zero
CSI-RS configuration of each considered transmission point is given independently
via RRC configuration message.
Citation List
Non-Patent Literature
Summary of Invention
Technical Problem
[0011] Now, as a promising technique for further improving the system performance of an
LTE system, there is inter-cell orthogonalization. For example, in an LTE-A system,
intra-cell orthogonalization is made possible by orthogonal multiple access on both
the uplink and the downlink. That is to say, on the downlink, orthogonalization is
provided between user terminals UE (User Equipment) in the frequency domain. On the
other hand, between cells, like in W-CDMA, interference randomization by one-cell
frequency reuse is fundamental.
[0012] So, in the 3GPP (3rd Generation Partnership Project), coordinated multiple-point
transmission/reception (CoMP) techniques are under study as techniques for realizing
inter-cell orthogonalization. In this CoMP transmission/reception, a plurality of
cells coordinate and perform signal processing for transmission and reception for
one user terminal UE or for a plurality of user terminals UE. By adopting these CoMP
transmission/reception techniques, improvement of throughput performance is expected,
especially with respect to user terminals UE located on cell edges.
[0013] In this way, in an LTE-A system, in addition to the mode of transmission to transmit
from one transmission point to user terminals, there is also a mode of transmission
to transmit from a plurality of transmission points to user terminals, so that it
is necessary to make user terminals feed back optimal channel quality information
(CSI) for each transmission mode.
[0014] The present invention has been made in view of the above, and it is therefore an
object of the present invention to provide a wireless communication system, a base
station apparatus, a user terminal, and a channel state information measurement method
which can allow a user terminal to feed back channel quality information that is optimal
for a mode of transmission from a plurality of transmission points.
Solution to Problem
[0015] The invention is defined by the appended claims. In the following, embodiments not
falling within the scope of the claims are to be understood as examples useful for
understanding the invention.
Technical Advantage of Invention
[0016] According to the present invention, it is possible to allow a user terminal to feed
back channel quality information that is optimal for a mode of transmission from a
plurality of transmission points. By this means, it is possible to improve throughput
and realize a highly efficient wireless communication system.
Brief Description of Drawings
[0017]
FIG. 1 is a diagram to show a CSI-RS pattern including zero-power CSI-RSs for measuring
interference;
FIG. 2 provides diagram for explaining a method of measuring interference signals;
FIG. 3 is a diagram for explaining a method of measuring desired signals;
FIG. 4 provides diagrams for explaining an example of CSI measurement;
FIG. 5 provides diagrams for explaining an example of CSI measurement;
FIG. 6 provides diagrams for explaining an example of CSI measurement;
FIG. 7 is a diagram to show subframes including resources for measuring desired signals
and resources for measuring interference signals;
FIG. 8 is a diagram to show examples of signaling of combinations of resources for
measuring desired signals and resources for measuring interference signals;
FIG. 9 is a diagram to show examples of signaling of combinations of resources for
measuring desired signals and resources for measuring interference signals;
FIG. 10 is a diagram to explain a system configuration of a wireless communication
system;
FIG. 11 is a diagram to explain an overall configuration of a base station apparatus;
FIG. 12 is a diagram to explain an overall configuration of a user terminal;
FIG. 13 is a functional block diagram of a base station apparatus; and
FIG. 14 is a functional block diagram of a user terminal.
Description of Embodiments
[0018] First, CSI-RS, which is one of the reference signals adopted in a successor system
of LTE (for example, Rel. 10), will be described. A CSI-RS is a reference signal that
is used to measure CSI, such as CQI (Channel Quality Indicator), PMI (Precoding Matrix
Indicator), and RI (Rank Indicator), as the channel state. Unlike CRSs that are allocated
to all subframes, CSI-RSs are allocated in a predetermined cycle -- for example, in
a 10-subframe cycle. Also, CSI-RSs are specified by parameters such as position, sequence
and transmission power. The positions of CSI-RSs include the subframe offset, the
cycle, and the subcarrier-symbol offset (index).
[0019] Note that non-zero-power CSI-RSs and zero-power CSI-RSs are defined as CSI-RSs. With
non-zero-power CSI-RSs, transmission power is distributed to the resources to which
the CSI-RSs are allocated, and, with zero-power CSI-RSs, transmission power is not
distributed to the resources to which the CSI-RSs are allocated (that is, the CSI-RSs
are "muted").
[0020] In one resource block, as defined in LTE, CSI-RSs are allocated not to overlap with
control signals such as the PDCCH (Physical Downlink Control Channel), user data such
as the PDSCH (Physical Downlink Shared Channel), and other reference signals such
as CRSs (Cell-specific Reference Signals) and DM-RSs (Demodulation - Reference Signals).
One resource block is formed with twelve subcarriers that are consecutive in the frequency
direction and fourteen symbols that are consecutive in the time axis direction. From
the perspective of suppressing PAPR, two resource elements that neighbor each other
in the time axis direction are allocated, as a set, to resources where CSI-RSs can
be allocated.
[0021] When CQIs are calculated with CSI-RSs, the accuracy of interference measurement becomes
important. By using CSI-RSs, which are user-specific reference signals, CSI-RSs from
a plurality of transmission points can be separated in a user terminal, so that interference
measurement based on CSI-RSs is promising. However, since the density of CSI-RSs in
one resource block is low according to the provisions of LTE (Rel. 10 LTE), it is
not possible to measure interference from other transmission points (other cells)
accurately.
[0022] So, the applicant has proposed, as shown in FIG. 1, adding zero power CSI-RSs for
use for interference measurement alone (hereinafter referred to as "interference measurement
zero power CSI-RSs"), and applying shifts in the frequency axis direction so that
the resources of interference measurement zero power CSI-RSs do not overlap between
transmission points. By this means, it is possible to measure interference signals
for calculation of CSI (Channel State Information) in user terminals, by using resource
elements (REs) in which the downlink shared data channel (PDSCH) is not transmitted.
In this case, interference measurement zero power CSI-RS patterns that vary for every
transmission point or for every plurality of transmission points are assigned.
[0023] By this means, it is possible to measure interference using both non-zero power CSI-RSs
(existing CSI-RSs with transmission power) and interference measurement zero-power
CSI-RSs, increase the number of CSI-RSs that can be used for interference measurement,
and improve the accuracy of interference measurement. Also, since transmission power
is zero with interference measurement zero-power CSI-RSs, signal components that are
received in resources where interference measurement zero power CSI-RSs are allocated
can be handled on an as-is basis, as interference components, and it is therefore
possible to reduce the processing load of interference measurement.
[0024] Here, an interference signal measurement method using interference measurement zero-power
CSI-RSs will be described. Here, a system configuration in which two radio base stations
serve as transmission point ("TP") #1 and TP #2 will be described as an example.
[0025] FIG. 2A shows a case where transmission is carried out from transmission points TP
#1 and TP #2 to a user terminal UE. Also, FIG. 2B shows an example of CSI-RS patterns
in which interference measurement zero power CSI-RSs are arranged. In FIG. 2B, the
subframe on the left side is a subframe to be transmitted from TP #1, and the subframe
on the right side is a subframe to be transmitted from TP #2.
[0026] As shown in FIG. 2B, if, in each subframe of TP #1 and TP #2, interference measurement
zero-power CSI-RSs are arranged in the REs that are the first and seventh REs in the
frequency direction and that are the tenth and eleventh REs in the time direction,
the PDSCH is not transmitted (hence zero power) in these REs of TP #1 and TP #2. Consequently,
in these REs, it is possible to measure interference signals from cells apart from
TP #1 and TP #2. Also, as shown in FIG. 2B, if, in the subframe of TP #1, interference
measurement zero power CSI-RSs are arranged in the REs that are the third and ninth
REs in the frequency direction and that are the tenth and eleventh REs in the time
direction, the PDSCH is not transmitted (hence zero power) in these REs of TP #1.
Consequently, in these REs, it is possible to measure interference signals from apart
from TP #1 (TP #2 + TP #1, and cells other than TP #2). Also, as shown in FIG. 2B,
if, in the subframe of TP #2, interference measurement zero power CSI-RSs are arranged
in the REs that are the fifth and eleventh REs in the frequency direction and that
are the tenth and eleventh REs in the time direction, the PDSCH is not transmitted
(hence zero power) in these REs of TP #2. Consequently, in these REs, it is possible
to measure interference signals from cells apart from TP #2 (TP #1 + TP #1, and cells
other than TP #2).
[0027] Next, a method of measuring desired signals using CSI-RSs will be described. Here,
a system configuration in which two radio base stations serve as transmission point
(TP) #1 and TP #2 will be described as an example.
[0028] FIG. 3 shows a case where transmission is carried out from transmission points TP
#1 and TP #2 to a user terminal UE. Also, FIG. 3 shows an example of CSI-RS patterns
in which CSI-RSs are arranged. In FIG. 3, the subframe on the left side is a subframe
to be transmitted from TP #1, and the subframe on the right side is a subframe to
be transmitted from TP #2.
[0029] As shown in FIG. 3, if, in each subframe of TP #1 and TP #2, CSI-RSs are arranged
in the REs that are the second and eighth REs in the frequency direction and that
are the tenth and eleventh REs in the time direction, in these REs, it is possible
to measure desired signals combining TP #1 and TP #2. Also, as shown in FIG. 3, if,
in the subframe of TP #1, CSI-RSs are arranged in the REs that are the fourth and
tenth REs in the frequency direction and that are the tenth and eleventh REs in the
time direction, in these REs, it is possible to measure desired signals for TP #1.
Also, as shown in FIG. 3, if, in the subframe of TP #2, CSI-RSs are arranged in the
REs that are the sixth and twelfth REs in the frequency direction and that are the
tenth and eleventh REs in the time direction, in these REs, it is possible to measure
desired signals for TP #2.
[0030] In this way, there are a plurality of methods of measuring interference signals and
measuring desired signals, so that a plurality of types of desired signal-to-interference
signal measurement results (Signal-to-Interference Ratio: SIR) can be achieved. The
present inventors have focused on this point, and arrived at the present invention
upon finding out that, when there are a plurality of transmission points (as in coordinated
multiple point transmission/reception (CoMP), for example), it is possible to allow
a user terminal to feed back optimal quality information (CSI, which is, for example,
CQI (Channel Quality Indicator)), by selecting an optimal desired signal-to-interference
signal measurement method (the method of measuring desired signal-to-interference
signal, to use in CSI measurement) depending on the mode of transmission, and, as
a result of this, improve the throughput of the system and improve the efficiency
of the system.
[0031] That is, a gist of the present invention is to, in each base station apparatus, determine
resource information about the resources to allocate the reference signals for measuring
desired signals to and the resources for measuring interference signals, and report
the resource information to a user terminal, and, in the user terminal, receive the
reported resource information, measure desired signals and interference signals based
on the resource information, and measure the channel state using the measurement results
in the measurement section, thereby allowing the user terminal to feed back channel
quality information that is optimal for a mode of transmission from a plurality of
transmission points. By this means, it is possible to improve throughput and realize
a highly efficient wireless communication system.
[0032] For example, CoMP transmission is a transmission mode from a plurality of transmission
points. First, downlink CoMP transmission will be described. Downlink CoMP transmission
includes coordinated scheduling/coordinated beamforming, and joint processing. Coordinated
scheduling/coordinated beamforming refers to the method of transmitting a shared data
channel to one user terminal UE from only one cell, and allocates radio resources
in the frequency/space domain taking into account interference from other cells and
interference against other cells. Meanwhile, joint processing refers to the method
of applying precoding and transmitting a shared data channel from a plurality of cells
simultaneously, and includes joint transmission to transmit a shared data channel
from a plurality of cells to one user terminal UE, and dynamic point selection (DPS)
to select one cell instantaneously and transmit a shared data channel. There is also
a transmission mode referred to as dynamic point blanking (DPB), which stops data
transmission in a certain region with respect to a transmission point that causes
interference.
[0033] With the present invention, an optimal method for measuring desired signals and a
method for measuring interference signals are selected in accordance with a mode of
transmission from a plurality of transmission points. First, the measurement method
to be used when joint transmission-type CoMP is applied will be described using FIG.
4.
[0034] As shown in FIG. 4A, in joint transmission-type CoMP transmission, shared data channel
signals are transmitted from a plurality of cells (TP #1 (connecting cell) and TP
#2 (coordinated cell)) to one user terminal UE. Consequently, as for desired signals,
it is preferable to measure desired signals combining TP #1 and TP #2. Also, as for
interference signals, it is preferable to measure interference signals from cells
(transmission points) other than TP #1 and TP #2. Consequently, as shown in FIG. 4B,
to measure interference signals, in each subframe of TP #1 and TP #2, interference
measurement zero power CSI-RSs are arranged in the REs that are the first and seventh
REs in the frequency direction and that are the tenth and eleventh REs in the time
direction (that is, interference measurement zero power CSI-RSs are arranged in the
same REs between the connecting cell (transmission point) and the coordinated cell
(transmission point)), and interference signals from cells other than TP #1 and TP
#2 are measured. Meanwhile, to measure desired signals, in each subframes of TP #1
and TP #2, CSI-RSs are arranged in the REs that are the second and eighth REs in the
frequency direction and that are the tenth and eleventh REs in the time direction
(that is, CSI-RSs are arranged in the same REs between the connecting cell (transmission
point) and the coordinated cell (transmission point)), and desired signals combining
TP #1 and TP #2 are measured.
[0035] Next, the measurement method to be used when dynamic point blanking-type CoMP is
applied will be described using FIG. 5. As shown in FIG. 5A, in dynamic point blanking-type
CoMP transmission, data transmission for a transmission point that causes interference
(in FIG. 5A, TP #2 (the coordinated cell (transmission point))) is stopped in a certain
region. Consequently, as for desired signals, it is preferable to measure desired
signals of TP #1 (the connecting cell (transmission point)). Also, as for interference
signals, it is preferable to measure interference signals from cells other than TP
#1 and TP #2. Consequently, as shown in FIG. 5B, to measure interference signals,
in each subframe of TP #1 and TP #2, interference measurement zero power CSI-RSs are
arranged in the REs that are the first and seventh REs in the frequency direction
and that are the tenth and eleventh REs in the time direction (that is, interference
measurement zero power CSI-RSs are arranged in the same REs between the connecting
cell (transmission point) and the coordinated cell (transmission point)), and interference
signals from cells other than TP #1 and TP #2 are measured. On the other hand, to
measure desired signals, in the subframe of TP #1, CSI-RSs are arranged in the REs
that are the fourth and tenth REs in the frequency direction and that are the tenth
and eleventh REs in the time direction (that is, CSI-RSs are arranged in the REs of
the connecting cell (transmission point)), and desired signals of TP #1 are measured.
[0036] Next, the measurement method to be used when CoMP is not applied will be described
using FIG. 6. FIG. 6A shows single-cell transmission to carry out transmission to
a user terminal from one transmission point TP #1. Consequently, as for desired signals,
it is preferable to measure desired signals of TP #1 (the connecting cell (transmission
point)). Also, as for interference signals, it is preferable to measure interference
signals from cells other than TP #1. Consequently, as shown in FIG. 6B, to measure
interference signals, in the subframe of TP #1, interference measurement zero-power
CSI-RSs are arranged in the REs that are the third and ninth REs in the frequency
direction and that are the tenth and eleventh REs in the time direction (that is,
interference measurement zero power CSI-RSs are arranged in the REs of the connecting
cell (transmission point)), and interference signals of cells other than TP #1 are
measured. Meanwhile, to measure desired signals, in the subframe of TP #1, CSI-RSs
are arranged in the REs that are the fourth and tenth REs in the frequency direction
and that are the tenth and eleventh REs in the time direction (CSI-RSs are arranged
in the REs of the connecting cell (transmission point)), and desired signals of TP
#1 are measured.
[0037] In this way, according to the present invention, when there are a plurality of transmission
points, an optimal desired signal-to-interference signal measurement method (the method
of measuring desired signal-to-interference signal, to use in CSI measurement) is
selected depending on the mode of transmission, so that it is possible to allow a
user terminal to feed back optimal quality information (CQI), and, as a result, improve
the throughput of the system and improve the efficiency of the system.
[0038] In this case, information about the method of measuring desired signals and the method
of measuring interference signals is signaled from a radio base station to a user
terminal. That is to say, to a user terminal, a radio base station signals information
about the REs to use for the measurement of desired signals (Signal Measurement Resources:
SMRs), information about the REs to use for the measurement of interference signals
(Interference Measurement Resources: IMRs), and information about the combinations
of SMRs and IMRs (one or a plurality of these pieces of information are signaled as
resource information about the resources to allocate reference signals for measuring
desired signals to and the resources for measuring interference signals). These pieces
of information may also be reported from a radio base station to a user terminal through
higher layer signaling (RRC signaling), or may be reported from a radio base station
to a user terminal dynamically through downlink control information (DCI). For example,
as shown in FIG. 5A, when dynamic point blanking-type CoMP is applied, when it is
desirable to feed back CSI, as shown in FIG. 5B, that is, signaling is sent semi-statically
or dynamically from a radio base station to a user terminal so that, in each subframe
of TP #1 and TP #2, the REs that are the first and seventh REs in the frequency direction
and that are the tenth and eleventh REs in the time direction are used to measure
interference signals, and, in the subframe of TP #1, the REs that are the fourth and
tenth REs in the frequency direction and that are the tenth and eleventh REs in the
time direction are used to measure desired signals.
[0039] By setting a plurality of combinations of SMRs and IMRs such as above, it becomes
possible to allow a user terminal to feed back a plurality of types of CSIs. In this
case, one or a plurality of SMRs and one or a plurality of IMRs are arranged in the
same subframe or in different subframes (configuration). For example, as shown in
FIG. 7, when there are two types of SMRs and IMRs (SMR #1, SMR #2, IMR #1 and IMR
#2) and SMR #1 and SMR #2 are present in the same subframe and IMR #1 and IMR #2 are
present in different subframes, signaling (CSI #1) to the effect of finding CSI with
the combination of SMR #1 and IMR #1, and signaling (CSI #2) to the effect of finding
CSI with the combination of SMR #2 and IMR #2 are reported from a radio base station
to a user terminal, so that it becomes possible to allow the user terminal to feed
back two kinds of CSIs (CSI #1 and CSI #2). Also, when there are two types of SMRs
and IMRs (SMR #1, SMR #2, IMR #1 and IMR #2) and the SMRs and IMRs are present in
the same subframe, signaling (CSI #1) to the effect of finding CSI with the combination
of SMR #1 and IMR #1, and signaling (CSI #2) to the effect of finding CSI from the
combination of SMR #2 and IMR #2 are reported from a radio base station to a user
terminal, so that it becomes possible to allow the user terminals to feed back two
kinds of CSIs (CSI #1 and CSI #2). Note that the patterns of arranging one or a plurality
of SMRs and one or a plurality of IMRs in the same subframe or in different subframes
are not particularly limited.
[0040] When combinations of SMRs and IMRs are reported, for example, if there are SMR #1,
IMR #1 and IMR #2, as shown in FIG. 8, it is possible to send signaling in two bits.
In FIG. 8, the bits "10" are used when measuring CSI with SMR #1 + IMR #1, the bits
"01" are used when measuring CSI with SMR #2 + IMR #2, the bits "11" are used when
measuring two types of CSIs with SMR #1 + IMR #1 and SMR #1 + IMR #2, and the bits
"00" are used when measuring CSI with SMR #1 and a conventional interference measurement
method (for example, interference measurement using CRSs). Note that FIG. 8 does not
limit the relationship between the combinations of SMRs and IMRs and the bits.
[0041] Also, when combinations of SMRs and IMRs are reported, if, for example, there are
SMR #1, SMR #2, IMR #1 and IMR #2, it is possible to send signaling in four bits,
as shown in FIG. 9. In FIG. 9, the bits "1010" are used when measuring CSI with SMR
#1 + IMR #1, the bits "0101" are used when measuring CSI with SMR #2 + IMR #2, the
bits "1000" are used when measuring CSI with SMR #1 and a conventional interference
measurement method (for example, interference measurement using CRSs), the bits "1011"
are used when measuring two types of CSIs with SMR #1 + IMR #1 and SMR #1 + IMR #2,
the bits "1101" are used when measuring two types of CSIs with SMR #1 + IMR #2 and
SMR #2 + IMR #2, and the bits "1111" are used when measuring four types of CSIs with
SMR #1 + IMR #1, SMR #1 + IMR #2, SMR #2 + IMR #1, and SMR #2 + IMR #2. Note that
FIG. 9 by no means limits the relationship between the combinations of SMRs and IMRs
and the bits.
[0042] A user terminal measures desired signals and interference signals using the REs that
are specified by the SMR information, the IMR information, and the information about
the combinations of SMRs and IMRs that are reported, and finds one or a plurality
of CSIs using the measurement results. The user terminal feeds back one or a plurality
of CSIs found in this way to a radio base station. Also, when the user terminal finds
CSI, the subframes to find interference signals in may be limited based on bitmap
information reported from the radio base station through higher layer signaling (for
example, RRC signaling). In this case, the user terminal finds CSI using the signaling
of combinations of SMRs and IMRs and the signaling to limit the subframes to find
interference signals in.
[0043] Now, a wireless communication system according to an embodiment of the present invention
will be described in detail. FIG. 10 is a diagram to explain a system configuration
of a wireless communication system according to the present embodiment. Note that
the wireless communication system shown in FIG. 10 is a system to accommodate, for
example, an LTE system or SUPER 3G. In this wireless communication system, carrier
aggregation to group a plurality of fundamental frequency blocks into one, where the
system band of the LTE system is one unit, is used. Also, this wireless communication
system may be referred to as "IMT-Advanced" or may be referred to as "4G."
[0044] As shown in FIG. 10, a wireless communication system 1 is configured to include base
station apparatuses 20A and 20B of individual transmission points, and user terminals
10 that communicate with these base station apparatuses 20A and 20B. The base station
apparatuses 20A and 20B are connected with a higher station apparatus 30, and this
higher station apparatus 30 is connected with a core network 40. Also, the base station
apparatuses 20A and 20B are connected with each other by wire connection or by wireless
connection. The user terminals 10 are able to communicate with the base station apparatuses
20A and 20B, which are transmission points. Note that the higher station apparatus
30 may be, for example, an access gateway apparatus, a radio network controller (RNC),
a mobility management entity (MME) and so on, but is by no means limited to these.
[0045] Although the user terminals 10 may include both existing terminals (Rel. 10 LTE)
and support terminals (for example, Rel. 11 LTE), the following description will be
given simply with respect to "user terminals," unless specified otherwise. Also, for
ease of explanation, user terminals 10 will be described to perform radio communication
with the base station apparatuses 20A and 20B.
[0046] In a wireless communication system 1, as radio access schemes, OFDMA (Orthogonal
Frequency Division Multiple Access) is adopted on the downlink, and SC-FDMA (Single-Carrier
Frequency Division Multiple Access) is adopted on the uplink, but the uplink radio
access scheme is by no means limited to this. OFDMA is a multi-carrier transmission
scheme to perform communication by dividing a frequency band into a plurality of narrow
frequency bands (subcarriers) and mapping data to each subcarrier. SC-FDMA is a single
carrier transmission scheme to reduce interference between terminals by dividing,
per terminal, the system band into bands formed with one or continuous resource blocks,
and allowing a plurality of terminals to use mutually different bands.
[0047] Here, communication channels will be described. Downlink communication channels include
a PDSCH (Physical Downlink Shared Channel), which is a downlink data channel used
by user terminals 10 on a shared basis, and downlink L1/L2 control channels (PDCCH,
PCFICH, and PHICH). Transmission data and higher control information are transmitted
by the PDSCH. PDSCH and PUSCH scheduling information and so on are transmitted by
the PDCCH (Physical Downlink Control CHannel). The number of OFDM symbols to use for
the PDCCH is transmitted by the PCFICH (Physical Control Format Indicator Channel).
HARQ ACK/NACK for the PUSCH are transmitted by the PHICH (Physical Hybrid-ARQ Indicator
Channel).
[0048] Uplink communication channels include a PUSCH (Physical Uplink Shared Channel), which
is an uplink data channel used by each user terminal on a shared basis, and a PUCCH
(Physical Uplink Control Channel), which is an uplink control channel. By means of
this PUSCH, transmission data and higher control information are transmitted. Also,
downlink channel state information (CSI (including CQI and so on)), ACK/NACK and so
on are transmitted by means of the PUCCH.
[0049] An overall configuration of a base station apparatus according to the present embodiment
will be described with reference to FIG. 11. Note that the base station apparatuses
20A and 20B have the same configuration and therefore will be described simply as
"base station apparatus 20." The base station apparatus 20 has a transmitting/receiving
antenna 201, an amplifying section 202, a transmitting/receiving section (reporting
section) 203, a baseband signal processing section 204, a call processing section
205, and a transmission path interface 206. Transmission data to be transmitted from
the base station apparatus 20 to the user terminal on the downlink is input from the
higher station apparatus 30 into the baseband signal processing section 204 via the
transmission path interface 206.
[0050] In the baseband signal processing section 204, a signal of a downlink data channel
is subjected to a PDCP layer process, division and coupling of transmission data,
RLC (Radio Link Control) layer transmission processes such as an RLC retransmission
control transmission process, MAC (Medium Access Control) retransmission control,
including, for example, an HARQ transmission process, scheduling, transport format
selection, channel coding, an inverse fast Fourier transform (IFFT) process, and a
precoding process. Furthermore, a signal of a physical downlink control channel, which
is a downlink control channel, is also subjected to transmission processes such as
channel coding and an inverse fast Fourier transform.
[0051] Also, the baseband signal processing section 204 reports control information for
allowing each terminal 10 to perform radio communication with the base station apparatus
20, to the user terminals 10 connected to the same transmission point, through a broadcast
channel. The information for allowing communication at the transmission point includes,
for example, the uplink or downlink system bandwidth, root sequence identification
information (root sequence index) for generating random access preamble signals in
the PRACH (Physical Random Access Channel), and so on.
[0052] The transmitting/receiving section 203 converts a baseband signal that is output
from the baseband signal processing section 204 into a radio frequency band. The amplifying
section 202 amplifies the radio frequency signal having been subjected to frequency
conversion, and outputs the result to the transmitting/receiving antenna 201.
[0053] Meanwhile, as for a signal to be transmitted from the user terminal 10 to the base
station apparatus 20 on the uplink, a radio frequency signal received by the transmitting/receiving
antenna 201 is amplified in the amplifying section 202, converted into a baseband
signal through frequency conversion in the transmitting/receiving section 203, and
input in the baseband signal processing section 204.
[0054] The baseband signal processing section 204 performs an FFT process, an IDFT process,
error correction decoding, a MAC retransmission control receiving process, and RLC
layer and PDCP layer receiving processes, of the transmission data that is included
in the baseband signal received on the uplink. The decoded signal is transferred to
the higher station apparatus 30 through the transmission path interface 206.
[0055] The call processing section 205 performs call processes such as setting up and releasing
communication channels, manages the state of the base station apparatus 20 and manages
the radio resources.
[0056] Next, an overall configuration of a user terminal according to the present embodiment
will be described with reference to FIG. 12. A user terminal 10 has a transmitting/receiving
antenna 101, an amplifying section 102, a transmitting/receiving section (receiving
section) 103, a baseband signal processing section 104, and an application section
105.
[0057] As for downlink data, a radio frequency signal that is received in the transmitting/receiving
antenna 101 is amplified in the amplifying section 102, and subjected to frequency
conversion and converted into a baseband signal in the transmitting/receiving section
103. This baseband signal is subjected to receiving processes such as an FFT process,
error correction decoding and retransmission control, in the baseband signal processing
section 104. In this downlink data, downlink transmission data is transferred to the
application section 105. The application section 105 performs processes related to
higher layers above the physical layer and the MAC layer. Also, in the downlink data,
broadcast information is also transferred to the application section 105.
[0058] Meanwhile, uplink transmission data is input from the application section 105 into
the baseband signal processing section 104. The baseband signal processing section
104 performs a mapping process, a retransmission control (HARQ) transmission process,
channel coding, a DFT process, and an IFFT process. The baseband signal that is output
from the baseband signal processing section 104 is converted into a radio frequency
band in the transmitting/receiving section 103. After that, the amplifying section
102 amplifies the radio frequency signal having been subjected to frequency conversion,
and transmits the result from the transmitting/receiving antenna 101.
[0059] The function blocks of the base station apparatus pertaining to the process of determining
the measurement REs for measuring desired signals and measuring interference signals
will be described with reference to FIG. 13. Note that each function block of FIG.
13 primarily relates to the baseband processing section shown in FIG. 11. Also, the
functional block diagram of FIG. 13 is simplified to explain the present invention,
but is assumed to have configurations which a baseband processing section should normally
have.
[0060] The base station apparatus 20 has, on the transmitting side, a measurement RE determining
section 401, a higher control information generating section 402, a downlink transmission
data generating section 403, a downlink control information generating section 404,
a CSI-RS generating section 405, a downlink transmission data coding/modulation section
406, and a downlink control information coding/modulation section 407. Also, the base
station apparatus 20 has a downlink channel multiplexing section 408, an IFFT section
409, and a CP adding section 410.
[0061] The measurement RE determining section 401 determines the resources (measurement
REs) to allocate the reference signals (CSI-RSs) for measuring desired signals to,
and the resources (measurement REs) for measuring interference signals. Also, the
measurement RE determining section 401 determines the combination of the resources
(measurement REs) to allocate the reference signals for measuring desired signals
to, and the resources (measurement REs) for measuring interference signals. These
resources (measurement REs) constitute resource information.
[0062] The measurement RE determining section 401 determines the above resource information
depending on the transmission mode of a plurality of base station apparatuses (transmission
points). For example, when the transmission mode is joint transmission-type coordinated
multiple-point transmission, as shown in FIG. 4B, the measurement RE determining section
401 determines, as for desired signals, the resources to measure desired signals combining
the connecting transmission point (TP #1) and the coordinated transmission point (TP
#2) (in FIG. 4B, the REs that are the second and eighth REs in the frequency direction
and that are the tenth and eleventh REs in the time direction in each subframe of
TP #1 and TP #2), and determines, as for interference signals, the resources (measurement
REs) to measure interference signals from transmission points other than the connecting
transmission point (TP #1) and the coordinated transmission point (TP #2) (in FIG.
4B, the REs that are the first and seventh REs in the frequency direction and that
are the tenth and eleventh REs in the time direction in each subframe of TP #1 and
TP #2).
[0063] Also, when the transmission mode is dynamic point blanking-type coordinated multiple-point
transmission, as shown in FIG. 5B, the measurement RE determining section 401 determines,
as for desired signals, the resources to measure desired signals of the connecting
transmission point (TP #1) (in FIG. 5B, the REs that are the fourth and tenth REs
in the frequency direction and that are the tenth and eleventh REs in the time direction
in the subframe of TP #1), and determines, as for interference signals, the resources
(measurement REs) to measure interference signals from transmission points other than
the connecting transmission point (TP #1) and the coordinated transmission point (TP
#2) (in FIG. 5B, the REs that are the first and seventh REs in the frequency direction
and that are the tenth and eleventh REs in the time direction in each subframe of
TP #1 and TP #2).
[0064] Also, when the transmission mode is single-cell transmission, as shown in FIG. 6B,
the measurement RE determining section 401 determines, as for desired signals, the
resources to measure desired signals for the connecting transmission point (TP #1)
(in FIG. 6B, the REs that are the fourth and tenth REs in the frequency direction
and that are the tenth and eleventh REs in the time direction in the subframe of TP
#1), and determines, as for interference signals, the resources (measurement REs)
to measure interference signals from transmission points other than the connecting
transmission point (TP #1) (in FIG. 6B, the REs that are the third and ninth REs in
the frequency direction and that are the tenth and eleventh REs in the time direction
in the subframe of TP #1).
[0065] When this resource information is signaled semi-statically to a user terminal, the
resource information is sent to the higher control information generating section
402 for higher layer signaling (for example, RRC signaling). Also, when this resource
information is signaled dynamically to a user terminal, the resource information is
sent to the downlink control information generating section 404 to be included in
downlink control information. Also, this resource information is sent to the CSI-RS
generating section 405 to generate CSI-RSs, and furthermore sent to the downlink transmission
data generating section 403 to make downlink transmission data zero power (muting)
(that is, to arrange interference measurement zero-power CSI-RSs).
[0066] The higher control information generating section 402 generates higher control information
to be transmitted and received by higher layer signaling (for example, RRC signaling),
and outputs the generated higher control information to the downlink transmission
data coding/modulation section 406. The higher control information generating section
402 generates higher control information, which includes the resource information
output from the measurement RE determining section 401. For example, the higher control
information generating section 402 generates information about the combination of
the resources (measurement REs) to allocate the reference signals (CSI-RSs) for measuring
desired signals to, and the resources (measurement REs) for measuring interference
signals, in the form of bit information such as the ones shown in FIG. 8 and FIG.
9.
[0067] The downlink transmission data generating section 403 generates downlink transmission
data, and outputs this downlink transmission data to the downlink transmission data
coding/modulation section 406. The downlink transmission data generating section 403
arranges interference measurement zero-power CSI-RSs (or executes muting) in accordance
with the resource information output form the measurement RE determining section 401.
[0068] The downlink control information generating section 404 generates downlink control
information, and outputs this downlink control information to the downlink control
information coding/modulation section 407. When signaling resource information to
a user terminal dynamically, the downlink control information generating section 404
generates downlink control information that includes the resource information. The
downlink transmission data coding/modulation section 406 performs channel coding and
data modulation of the downlink transmission data and the higher control information,
and outputs the results to the downlink channel multiplexing section 408. The downlink
control information coding/modulation section 407 performs channel coding and data
modulation of the downlink control information, and outputs the result to the downlink
channel multiplexing section 408.
[0069] The CSI-RS generating section 405 generates a CSI-RS in accordance with the resource
information output from the measurement RE determining section 401, and outputs this
CSI-RS to the downlink channel multiplexing section 408.
[0070] The downlink channel multiplexing section 408 combines the downlink control information,
the CSI-RS, the higher control information and the downlink transmission data, and
generates a transmission signal. The downlink channel multiplexing section 408 outputs
the generated transmission signal to the IFFT section 409. The IFFT section 409 applies
an inverse fast Fourier transform to the transmission signal and converts the transmission
signal from a frequency domain signal to a time domain signal. The transmission signal
after the IFFT is output to a CP adding section 410. The CP adding section 410 adds
CPs (Cyclic Prefixes) to the transmission signal after the IFFT, and outputs the transmission
signal, to which CPs have been added, to the amplifying section 202 shown in FIG.
11.
[0071] Now, the function blocks of a user terminal pertaining to the channel state measurement
process according to the present invention will be described with reference to FIG.
14. Note that each function block of FIG. 14 primarily relates to the baseband processing
section 104 shown in FIG. 12. Also, the function blocks of FIG. 12 are simplified
to explain the present invention, but are assumed to have configurations which a baseband
processing section should normally have.
[0072] The user terminal 10 has, on the receiving side, a CP removing section 301, an FFT
section 302, a downlink channel demultiplexing section 303, a downlink control information
receiving section 304, a downlink transmission data receiving section 305, an interference
signal measurement section 306, a channel measurement section 307, and a CQI calculation
section 308.
[0073] A transmission signal that is transmitted from the base station apparatus 20 is received
in the transmitting/receiving antenna 101 shown in FIG. 12, and output to the CP removing
section 301. The CP removing section 301 removes the CPs from the received signal
and outputs the result to the FFT section 302. The FFT section 302 performs a fast
Fourier transform (FFT) of the signal, from which the CPs have been removed, and converts
the time domain signal into a frequency domain signal. The FFT section 302 outputs
the signal having been converted into a frequency domain signal to the downlink channel
demultiplexing section 303.
[0074] The downlink channel demultiplexing section 303 demultiplexes the downlink channel
signal into the downlink control information, the downlink transmission data, and
the CSI-RS. The downlink channel demultiplexing section 303 outputs the downlink control
information to the downlink control information receiving section 304, outputs the
downlink transmission data and the higher control information to the downlink transmission
data receiving section 305, and outputs the CSI-RS to the channel measurement section
307.
[0075] The downlink control information receiving section 304 demodulates the downlink control
information, and outputs the demodulated downlink control information to the downlink
transmission data receiving section 305. The downlink transmission data receiving
section 305 demodulates the downlink transmission data using the demodulated downlink
control information. At this time, the downlink transmission data receiving section
305 specifies the desired signal measurement REs (CSI-RS resources) and the interference
signal measurement REs based on the resource information included in the higher control
information. The downlink transmission data receiving section 305 demodulates the
user data, not including the desired signal measurement REs (CSI-RS resources) and
the interference signal measurement REs. Also, the downlink transmission data receiving
section 305 outputs the higher control information included in the downlink transmission
data, to the interference signal measurement section 306.
[0076] The interference signal measurement section 306 measures interference signals in
the interference signal measurement REs based on the resource information included
in the higher control information (or downlink control information).
[0077] When, for example, the transmission mode is joint transmission-type coordinated multiple-point
transmission, as shown in FIG. 4B, the interference signal measurement section 306
measures interference signals with the REs that are the first and seventh REs in the
frequency direction and that are the tenth and eleventh REs in the time direction,
in each subframe of TP #1 and TP #2. Also, when, for example, the transmission mode
is dynamic point blanking-type coordinated multiple-point transmission, as shown in
FIG. 5B, the interference signal measurement section 306 measures interference signals
with the REs that are the first and seventh REs in the frequency direction and that
are the tenth and eleventh REs in the time direction, in each subframe of TP #1 and
TP #2. Also, when, for example, the transmission mode is single-cell transmission,
as shown in FIG. 6B, the interference signal measurement section 306 measures interference
signals with the REs that are the third and ninth REs in the frequency direction and
that are the tenth and eleventh REs in the time direction, in the subframe of TP #1.
[0078] The interference signal measurement section 306 measures interference signals in
this way, and averages the measurement results of all resource blocks. The averaged
interference signal measurement result is reported to the CQI calculation section
308.
[0079] The channel measurement section 307 specifies the desired signal measurement REs
(CSI-RS resources) based on the resource information included in the higher control
information (or downlink control information), and measures desired signals with the
desired signal measurement REs (CSI-RS resources).
[0080] When, for example, the transmission mode is joint transmission-type coordinated multiple-point
transmission, as shown in FIG. 4B, the channel measurement section 307 measures desired
signals with the REs that are the second and eighth REs in the frequency direction
and that are the tenth and eleventh REs in the time direction in the each subframe
of TP #1 and TP #2. Also, when, for example, the transmission mode is dynamic point
blanking-type coordinated multiple-point transmission, as shown in FIG. 5B, the channel
measurement section 307 measures desired signals with the REs that are the fourth
and tenth REs in the frequency direction and that are the tenth and eleventh REs in
the time direction in the subframe of TP #1. Also, when, for example, the transmission
mode is single-cell transmission, as shown in FIG. 6B, the channel measurement section
307 measures desired signals in the REs that are the fourth and tenth REs in the frequency
direction and that are the tenth and eleventh REs in the time direction in the subframe
of TP #1.
[0081] The channel measurement section 307 reports channel measurement values to the CQI
calculation section 308. The CQI calculation section 308 calculates the channel state
(CQI) based on the interference measurement result reported from the interference
signal measurement section 306, the channel measurement result reported from the channel
measurement section 307, and the feedback mode. Note that the feedback mode may be
set to any one of wideband CQI, subband CQI, and best-M average. The CQI calculated
in the CQI calculation section 308 is reported to the base station apparatus 20 as
feedback information.
[0082] In the above description, the CSI-RS patterns shown in FIG. 1 to FIG. 6 follow the
CSI-RS patterns defined in LTE-A (Rel. 10 LTE) on an as-is basis (in other words,
"re-use" them). Consequently, it is possible to signal the resources to be muted to
existing terminals (Rel. 10 LTE) within the range of the capacities of the terminals
(the functions which the terminals support).
1. Drahtloses Kommunikationssystem, umfassend eine Basisstationsvorrichtung (20), die
ein Referenzsignal zum Messen eines Kanalzustands überträgt, und ein Benutzerendgerät
(10), das sich mit der Basisstationsvorrichtung verbindet, wobei:
ein Übertragungsmodus koordinierte Mehrpunktübertragung ist,
die Basisstationsvorrichtung (20) umfasst:
einen Bestimmungsabschnitt (401), der Informationen zu einer Ressource für das Referenzsignal
und einer Ressource für Interferenzmessungen bestimmt; und
einen Berichtungsabschnitt (203), der die Informationen an das Benutzerendgerät (10)
berichtet; und
das Benutzerendgerät (10) umfasst:
einen Messabschnitt (307), der die Informationen als eine Basis verwendet, um Kanalmessungen
unter Verwendung der Ressource für das Referenzsignal abzuleiten, und Interferenzmessungen
unter Verwendung der Ressource für Interferenzmessungen abzuleiten; und
einen Berechnungsabschnitt (308), der eine Kanalqualität unter Verwendung der Kanalmessungen
und der Interferenzmessungen berechnet,
die Informationen über höhere Schichten signalisiert werden, und
die Ressource für das Referenzsignal ein Nicht-Nullleistungs-Kanalzustandsinformationen-Referenzsignal,
Nicht-Nullleistungs-CSI-RS, einschließt, und die Ressource für Interferenzmessungen
ein Nullleistungs-Kanalzustandsinformationen-Referenzsignal, Nullleistungs-CSI-RS,
zur alleinigen Verwendung für Interferenzmessung einschließt.
2. Drahtloses Kommunikationssystem nach Anspruch 1, wobei Ressourcen für Nullleistungs-CSI-RS
für die Interferenzmessungen zwischen Übertragungspunkten nicht überlappen.
3. Drahtloses Kommunikationssystem nach einem der Ansprüche 1 bis 2, wobei wenn der Übertragungsmodus
koordinierte Mehrpunktübertragung vom gemeinsamen Übertragungstyp ist, die Ressource
für das Referenzsignal dazu bestimmt ist, ein gewünschtes Signal zu messen, das einen
verbindenden Übertragungspunkt und einen koordinierten Übertragungspunkt kombiniert,
und die Ressource für Interferenzmessungen dazu bestimmt ist, Interferenz von einem
anderen Übertragungspunkt als dem verbindenden Übertragungspunkt und dem koordinierten
Übertragungspunkt zu messen.
4. Drahtloses Kommunikationssystem nach einem der Ansprüche 1 bis 2, wobei wenn der Übertragungsmodus
koordinierte Mehrpunktübertragung vom Typ mit dynamischer Punktausblendung ist, die
Ressource für das Referenzsignal dazu bestimmt ist, ein gewünschtes Signal eines verbindenden
Übertragungspunkts zu messen, und die Ressource für Interferenzmessungen dazu bestimmt
ist, Interferenz von einem anderen Übertragungspunkt als dem verbindenden Übertragungspunkt
und einem koordinierten Übertragungspunkt zu messen.
5. Basisstationsvorrichtung (20) in einem drahtlosen Kommunikationssystem, das die Basisstationsvorrichtung
(20), die ein Referenzsignal zum Messen eines Kanalzustands überträgt, und ein Benutzerendgerät
(10) umfasst, das sich mit der Basisstationsvorrichtung verbindet,
wobei ein Übertragungsmodus koordinierte Mehrpunktübertragung ist, und
wobei die Basisstationsvorrichtung (20) umfasst:
einen Bestimmungsabschnitt (401), der Informationen zu einer Ressource für das Referenzsignal
und einer Ressource für Interferenzmessungen bestimmt; und
einen Berichtungsabschnitt (203), der die Informationen an das Benutzerendgerät berichtet;
wobei die Informationen über höhere Schichten signalisiert werden, und
die Ressource für das Referenzsignal ein Nicht-Nullleistungs-CSI-RS einschließt, und
die Ressource für Interferenzmessungen ein Nullleistungs-CSI-RS zur alleinigen Verwendung
für Interferenzmessung einschließt.
6. Benutzerendgerät (10) in einem drahtlosen Kommunikationssystem, das eine Basisstationsvorrichtung
(20), die ein Referenzsignal zum Messen eines Kanalzustands überträgt, und das Benutzerendgerät
(10) umfasst, das sich mit der Basisstationsvorrichtung (20) verbindet,
wobei ein Übertragungsmodus koordinierte Mehrpunktübertragung ist, und
das Benutzerendgerät (10) umfasst:
einen Messabschnitt (307), der Informationen zu einer Ressource für das Referenzsignal
und einer Ressource für Interferenzmessungen als eine Basis verwendet, um Kanalmessungen
unter Verwendung der Ressource für das Referenzsignal abzuleiten, und Interferenzmessungen
unter Verwendung der Ressource für Interferenzmessungen abzuleiten; und
einen Berechnungsabschnitt (308), der eine Kanalqualität unter Verwendung der Kanalmessungen
und der Interferenzmessungen berechnet, und
wobei die Informationen über höhere Schichten signalisiert werden, und
die Ressource für das Referenzsignal ein Nicht-Nullleistungs-CSI-RS einschließt, und
die Ressource für Interferenzmessungen ein Nullleistungs-CSI-RS zur alleinigen Verwendung
für Interferenzmessung einschließt.
7. Kanalzustandsinformationen-Messverfahren in einem drahtlosen Kommunikationssystem,
das eine Basisstationsvorrichtung (20), die ein Referenzsignal zum Messen eines Kanalzustands
überträgt, und ein Benutzerendgerät (10) umfasst, das sich mit der Basisstationsvorrichtung
(20) verbindet, wobei ein Übertragungsmodus koordinierte Mehrpunktübertragung ist,
wobei das Kanalzustandsinformationen-Messverfahren die Schritte umfasst des:
an der Basisstationsvorrichtung (20):
Bestimmens von Informationen zu einer Ressource für das Referenzsignal und einer Ressource
für Interferenzmessungen; und
Berichtens der Informationen an das Benutzerendgerät (10); und
am Benutzerendgerät:
Verwendens der Informationen als eine Basis, um Kanalmessungen unter Verwendung der
Ressource für das Referenzsignal abzuleiten, und Interferenzmessungen unter Verwendung
der Ressource für Interferenzmessungen abzuleiten; und
Berechnens einer Kanalqualität unter Verwendung der Kanalmessungen und der Interferenzmessungen,
und
wobei die Informationen über höhere Schichten signalisiert werden, und
die Ressource für das Referenzsignal ein Nicht-Nullleistungs-CSI-RS einschließt, und
die Ressource für Interferenzmessungen ein Nullleistungs-CSI-RS zur alleinigen Verwendung
für Interferenzmessung einschließt.